Parade

Ask Marilyn: What Do Airplane Inspections Really Accomplish?

David Naumann of Tuscaloosa, Alabama, writes:

Marilyn: I’m a commercial pilot. From day one, all pilots are taught the importance of doing a thorough preflight check of the aircraft. This includes visually inspecting everything you can and exercising every switch, knob, and control in the cockpit. In its simplest form, a manual check may mean pushing a button and seeing that a light goes on.

My question is this: Say the light goes on. Fine, but every part has a lifespan, including this button. It will work, say, 7,354 times and fail the 7,355th time. In other words, I know the part worked the last time I checked it, but this tells me nothing about the next time. So what am I accomplishing with this test? (Don’t get me wrong: I do all the required tests on my aircraft before each flight, but I sometimes wonder about them!) Marilyn responds:

As I see it, the test informs you about the past, not the future. When the light goes on, it tells you that nothing has gone wrong since the last time you flew that aircraft, when you walked away and left it in the care of others. So the reason you conduct the test is for that rare instance when the light doesn’t go on. This tells you something has changed since you last landed, and you can’t fly the craft again until you find out what happened and fix it.